1. Field of the Invention
The invention relates to a fuel filter for an internal combustion engine. More particularly, the invention relates to a fuel filter that has a replaceable filter and an electric switch that indicates an “OK” and a “not OK” operating state of the fuel filter.
2. Description of the Prior Art
Fuel filters with replaceable filter inserts are known in the field of art. Conventional fuel filters have a replaceable filter insert and a cap that closes the filter housing. It is possible to remove a used filter insert and replace it with a new one when the cap is open. Convention fuel filters have a water collection chamber in a lower end of the housing, or in a collection cap. The specific weight of water is greater than that of fuel, and this allows water to be separated from the fuel and collected in the water collection chamber.
The increasing precision of fuel injection systems results in an increasing sensitivity of components and fuel lines to contaminants in the fuel. It is particularly serious for the operation of the vehicle, if, in the course of performing a filter change, the filter housing is closed without a new or suitable filter insert having been installed. The wrong filter insert could have incorrect dimensions or have a filter surface that is unsuitable for the type of fuel that is used. Having no filter insert or an improper filter insert installed in the fuel filter can have serious consequences for the fuel injection system, because unfiltered or insufficiently filtered fuel, dirt particles, and other contaminants can now pass into the fuel-injection system,
One of the undesirable fuel contaminants is water. The volume in the fuel tank includes air, and the fluctuations in temperature, such as occur, for example, as a result of temperature differences between nighttime and daytime temperatures, cause moisture to drop out of the air as condensation when the temperature drops. The formation of condensation is not something that the operator of the engine or maintenance personnel can prevent, and so, the presence of water in fuel is a problem that must be resolved within the internal combustion engine. For this reason, as a safety measure, conventional fuel filters are equipped with a water collection chamber for collecting the water condensation and a water level sensor, which sends a signal when the level of water in the collection chamber has reached a predetermined high level. The water level sensor has two electrical contacts that are spaced a distance apart from one another and placed relatively high up in the collection chamber, at a level that corresponds to a specified upper level of water that is deemed acceptable for operation of the filter system. The electrical conductivity of water differs from that of fuel and, when the water level in the water collection chamber rises above the specified level, the water creates a bridge between the two contacts, thereby significantly altering the electrical resistance between the two contacts. When the two conductors are electrically connected to one another by means of the water that is collected in the fuel filter, the value of the electrical resistance is designated the “short-circuit value”, and, when the two conductors are separated from one another or are connected to one another only by the fuel or by insulating materials, the value of the electrical resistance is designated the so-called “insulation value”.
The change from the “insulation value”, which corresponds to the normal operation of the fuel filter, to the “short-circuit value”, which corresponds to a too-high water content in the fuel filter, is measured and evaluated by an electronic switch, whereby the switch, for example, may be part of an electronic motor control unit. In the field of automobile construction, it is well-known to trigger an optical and/or acoustical signal within the driver's perceptual range, when water in the fuel filter reaches a defined level.
It is also known, to provide a more comprehensive safety measure to protect the internal combustion engine. For example, such a safety measure automatically prevents the motor from being started, should an unacceptably high level of water in the fuel filter be ascertained. This prevents water from reaching the clean side of the fuel filter and getting into the fuel injection system. Draining the water from the fuel filter system eliminates the “short circuit” caused by the water between the two contacts of the water level sensor and the electrical resistance between the two contacts reverts to its higher value. The higher electrical resistance is then detected by the electronic control, which now allows the engine to be started.
It is well-known in the field, irrespective of the aforementioned water level sensors, to provide temperature sensors or pressure sensors in the fuel filter. Depending upon the construction of the filter, one, two, or all three of the aforementioned sensor types may be provided in one fuel filter.
The task of the invention is to improve a generic fuel filter and specify a process in a way that enables the fuel filter to provide better protection for the engine associated with the fuel filter, with the least possible technical complexity and expense.